Study Of Square Concrete-encased CFST Columns Under Compression And Torsion

Concrete-encased CFST column is a type of structure,developed on the concrete filled steel tube and reinforced concrete,with the advantages of high bearing capacity,excellent fire resistance,good seismic effect and so on.The study on mechanics properties under compression and torsion of concrete-encased CFST columns is to make up for the deficiency that there is still lacking of it.For the development and practical application of concrete-encased CFST columns,the wider and the deeper studies has great significance.In this article we used experiment and simulation methods to study the mechanical behavior of concrete-encased CFST columns under torsion or compression and torsion.Finally,on the basis of experiment and simulation,referring to related papers and summarizing the previous research on behavior of concrete filled steel tube and reinforced concrete under torsion or torsion and compression,i presented a practical formula to calculating the ultimate bearing capacity of concrete-encased CFST columns under torsion or compression and torsion.The formula simplifies calculation process and provides reference for the designation of specimens.The specific works are carried out in the following aspects in this paper:Carried out 10 mechnics properties experiments under torsion or compression and torsion to studies the mechanics properties,destruction form,the ultimate bearing capacity under torsion or compression and torsion,torsion stiffness and the important parameters effect lows of square concrete-encased CFST columns.On the basis of the material properties measured in the experiments,the finite element calculation model under torsion or compression and torsion is established,basing on the actual situation,by using the usual finite element analysis software ABAQUS.The whole force process of the specimens were calculated by the model.We found that the results and full process curve of torque-angle of calculations agreed well with experiments and verifies the rationality of the finite element model.Parametric analysis of mechanical properties of concrete-encased CFST columns under torsion or compression and torsion is carried out by using the method of controling variables on the model,including the precent of concrete filled steel tube to specimens,the precent of tube to concrete filled steel tube,strength of outer concrete,strength of inner concrete,strength of tube,strength of longitudinal and strength of stiffup.A practical method for calculating the ultimate bearing capacity of concrete-encased CFST columns under torsion or compression and torsion is proposed.Compared the calculation results with simulation results and experiment results,all the resultant errors are within 10%and the discreteness is small.The comparison results showed that they are in good agreement and the caculation results is lower than others.The reliability of the practical formula for the ultimate bearing capacity was verified.